Field of the Invention
The present invention relates to a focused ion beam system for directing a focused ion beam at a sample or a workpiece to process it and also to a method of making a focal adjustment of the ion beam.
Description of Related Art
A known technique for making a focal adjustment in a focused ion beam system consists of varying the amount of adjustment of a beam optical system to produce various states, taking and displaying final images of a sample under these states, and repeating an operation for selecting a clear image, thus adjusting the focus (see, for example, JP-A-2000-048756). Another known technique for making a focal adjustment consists of selecting a signal arising from edge structures of a sample and determining a focal position at which the signal becomes sharpest.
In the above-described known method, it is necessary to scan the surface of a sample with an ion beam in order to obtain a final image and, therefore, etching of the ion beam damages a wide area on the sample. In the known method employing a signal arising from edge structures has the problem that a focal adjustment cannot be made unless any structure exists on the sample.